Answer
$0.405 \tau$
Work Step by Step
The formula for capacitor discharge is $Q = q_0 * e^\frac{-x}{\tau}$. To find the point at which the capacitor has lost the first third of charge, we set $e^{\frac{-x}{\tau}}= \frac{2}{3}$.This occurs when $\frac{x}{\tau} = \ln 1.5 = 0.405$. Therefore, the answer is $0.405 \tau$.
